Holyfield has perfected the art of headbutting. You can watch every fight that he's ever been in since hitting the big screen, and he is doing it. It's actually more intentional than it looks. I'm sure he has worked on his technique just as he has worked on punches and footwork. Even earlier Cruiserweight fights. If you actually look at what he's doing with his head while he comes forward to the inside, he's always dropping it, and ramming it straight into his opponents face. Very slick.